A photolithographic method has been utilized in a production of integrated circuits. Recently the photolithographic method is utilized in a production of the print circuit boards to form patterns of circuits on a board.
The photolithographic method utilizes an original plate on which the pattern to be printed is drawn and a light is supplied through the original plate on a print circuit board to form the same pattern as the plate thereon. Glass plates are used as the original plate in manufacturing integrated circuits because high accuracy is required. Film masks are usually utilized however in producing print circuit boards because rather low accuracy is allowable in this field.
When a film mask is employed as an original plate, it is very important to closely contact the film mask against the print circuit board. If the contact between the film masks and the board is incomplete the pattern projected on the board become incomplete. In particular the width of the pattern on the board become wider than the original pattern. In the prior art the gap between the film and the board is vacuumed after abutting them so that they can be closely contacted each other.
However it is difficult to substantially vacuum the gap so that the film is almost completely in contact with the board. Furthermore the cost for vacuuming is high and the apparatus therefor is complex and expensive.